Binary String pattern matching

[Valdimar Kristjánsson]

You could reverse it first and then match on the reversed symbol:

Data from the provider:

> Reversed = list_to_binary(lists:reverse(binary_to_list(<<"1234EUR">>))).



Reverse the Currency name in the match

>  currency_to_credits({cur, <<"RUE", Reversed/binary>>}, Acc) ->
>    {eur, Acc + A};


Probably not the most performant but at least it solves the problem.

Best,
nisbus

On Thu, Dec 10, 2020 at 8:16 AM Java House <java4dev@REDACTED> wrote:

> Hi
>
> yes the binary string is of the format <<"xxx">>
>
> <<"3123CHF">>
>> <<"341424343EUR">>
>> <<"14143US">>
>>
>  Thank you for the answer.
> So is there any other way?
> erlang provides the binary_to_list, is there any way to achieve the same
> with a list becasue I tried similare patterns with list and it does not
> work e.g
> [V|T] this will always match the first character of the string to V
> and [V|"CHF"] does not work neither.
>
> Best
> Nikolas
>
> Στις Τετ, 9 Δεκ 2020 στις 7:58 μ.μ., ο/η kuna.prime <
> kuna.prime@REDACTED> έγραψε:
>
>> HI,
>>
>> first of all binary string is of form <<"3123CHF">> and not <<3123CHF>>
>> i'm just stating it in case there was a mistake in the first mail
>>
>> to answer your questio in order to pattern match you need to know the
>> size of field you are matching so
>>
>> <<X:4/binary, "CHF">> = <<"3123CHF">>.
>>
>> will match fist 4 bytes and interpret that as new binary (X).
>>
>>
>> Sent with ProtonMail <https://protonmail.com> Secure Email.
>>
>> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
>> On Wednesday, December 9, 2020 7:28 PM, Java House <java4dev@REDACTED>
>> wrote:
>>
>> there is a typo in the example
>> currrency_to_credits({cur, << Value , "CHF">>}, Acc)
>>   when Value >= <<"1000">>, Value =< <<"10000">> ->
>>      {chf, Acc + Value };
>> currrency_to_credits({cur, << Value , "EUR">>}, Acc)
>>   when Value >= <<"1000">>, Value =< <<"10000">> ->
>>      {eur, Acc + Value };
>> currrency_to_credits({cur, << Value , "US">>}, Acc)
>>   when Value >= <<"1000">>, Value =< <<"10000">> ->
>>      {us, Acc + Value };
>>
>> Στις Τετ, 9 Δεκ 2020 στις 7:17 μ.μ., ο/η Java House <java4dev@REDACTED>
>> έγραψε:
>>
>>> Hello all
>>>
>>> I am learning Erlang and have stuck to the following problem.
>>> How to write a function with pattern matching when the parameter is a
>>> binary string.
>>>
>>> I have a list of binary strings e.g.
>>> <<3123CHF>>
>>> <<341424343EUR>>
>>> <<14143US>>
>>>
>>> I am trying to create a function that matches according to a pattern.
>>>
>>> currrency_to_credits({cur, <<A, "CHF">>}, Acc)
>>>   when Value >= <<"1000">>, Value =< <<"10000">> ->
>>>      {chf, Acc + A};
>>> currrency_to_credits({cur, <<A, "EUR">>}, Acc)
>>>   when Value >= <<"1000">>, Value =< <<"10000">> ->
>>>      {eur, Acc + A};
>>> currrency_to_credits({cur, <<A, "US">>}, Acc)
>>>   when Value >= <<"1000">>, Value =< <<"10000">> ->
>>>      {us, Acc + A};
>>>
>>> But this does not seem to be the right way.
>>> How can I create a pattern for binary string?
>>> will it work better for list string? How?
>>>
>>> Thank you
>>> Nikolas
>>>
>>
>>
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